This application claims the priority of German application 100 12 891.2, filed Mar. 16, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a two-piece wheel for a motor vehicle having hollow spokes arranged in a rim spider between air openings. The wheel includes a core made of metal foam which remains in the rim spider, and a friction weld between two spaced weld ring surfaces of the rim spider and the rim by which the rim spider and the rim are connected with one another.
A vehicle wheel which is produced in two pieces in a casting die tool, or in which a rim spider is cast and a rim can be produced in a different manner, is known from German Patent Document DE 41 38 558 A1. Connection of the two wheel pieces, such as the rim spider and the rim, takes place by friction welding. Two spaced weld ring surfaces are provided in the rim spider, on which opposite weld ring surfaces of the rim are arranged. Hollow spokes are provided in the wheel. These hollow spokes are formed by a sand core, which is removed after casting. A one-piece vehicle wheel which has metal foam cores remaining in hollow spokes is further known from German Patent Document DE 197 54 959 A1.
It is one object of the invention to provide a two-piece vehicle wheel having a metal foam core which can be integrated in a simple manner in the wheel, and in which wheel pieces can consist of different materials and can easily be connected in a substance-adhering manner.
It is advantageous, for weight reasons, to provide a two-piece wheel with hollow spokes and metal foam cores remaining in hollow spaces. The walls of the hollow spokes and the walls of additional hollow spaces or ring spaces in the wheel can be designed to be thinner because the metal foam core provides the inside of the wheel with a certain stability.
Production of the rim spider in the casting die tool is determined by the support of the metal foam cores in the top core, because it forms the hollow spaces of the spokes in a shaping manner.
For this purpose, a free portion of the metal foam core is supported in a plane at the base of a top core of the casting die tool. The weld ring surfaces of the rim spider are enclosed in this partial core, and the partial core extends to the plane of a hump surface of the rim spider. In this plane, division of the casting die tool into the top core and a bottom core takes place.
A favorable heat balance can be achieved during casting and in a cooling phase by providing the casting die tool with so-called slides which are arranged on the circumference side of the metal foam core or of the rim spider.
Connection of the rim spider with the rim by way of a known friction weld advantageously results in a variety of combination possibilities with respect to the material selection for the rim spider and the rim as well as the metal foam core. The walls surrounding the core, therefore, can have different thicknesses; alternatively, ribs, webs, and similar reinforcements can be provided inside the hollow spokes in addition to the metal foam core.